In general, epoxy resin compositions that comprise a curable epoxy resin, a curing agent and various additives, are superior in moldability, adherence, electric properties, mechanical properties, and moisture resistance as compared to other conventional thermosetting resins. Therefore, epoxy resin compositions are often used for the encapsulation of semiconductor devices.
The general trend in the advanced semiconductor device technology is to reduce the size and thickness of packages, although semiconductor elements have become of larger size. If such semiconductor elements are encapsulated with conventional epoxy resin compositions, larger stresses are applied to the semiconductor elements due to the difference in dimensional change between the elements and the compositions caused by changes in temperature. In addition, more or less moisture absorption can occur prior to soldering, causing cracks in the packages.
To overcome these problems, the same assignee as the present invention previously proposed several solutions; for example: an epoxy resin composition having an organopoly. siloxane blended in a curable epoxy resin as disclosed in U.S. Pat. No. 4,376,147, an epoxy resin composition having blended therein a block copolymer of an aromatic polymer and an organopolysiloxane as disclosed in U.S. Pat. No. 4,902,732, and a semiconductor device encapsulated with a composition comprising a novolak type phenol resin or triphenolalkane type phenol resin and an organopolysiloxane as disclosed in Japanese Patent Application Kokai No. 226951/1988. These epoxy resin compositions are of less stressing nature. Nevertheless, even these compositions cannot meet all the requirements for the encapsulation of advanced semiconductor devices.
At present, there is a need for the development of a semiconductor encapsulating resin composition which shows improved flow behavior upon casting and forms cured products having improved properties including mechanical strength such as flexural strength and flexural modulus, a high glass transition temperature, and moisture resistance in addition to the less stressing nature.